[ Eq(Derivative(x1, t), ((-1)*k4*k5*x3*x1 + (-1)*k4*k7*x4*x1 + (-1)*k4*k2*x1 + 1*k4*k12)/k4),
  Eq(Derivative(x2, t), (1*k4*k5*x3*x1 + 1*k4*k7*x4*x1 + (-1)*k4*k1*x2 + (-1)*k4*(k8*x2*k14 - k9*k15) + 1*k4*k10*k15)/k4),
  Eq(Derivative(x3, t), ((-1)*k4*k6*x2**k3*x3 + (-1)*k4*k1*x3 + 1*k4*k11)/k4),
  Eq(Derivative(x4, t), (1*k4*k6*x2**k3*x3 + (-1)*k4*k1*x4)/k4),
  Eq(Derivative(x5, t), 0),
  Eq(Derivative(x6, t), 0) ]